JR Will NOT work without a battery in the slave. The cord connecting a JR master and JR slave does not carry power. I know this because i use exclusively JR products. I will not comment on any other system that I do not have first hand knowledge of.
However, i also know that JR will work as a slave without a crystal as I took the crystal out of my quatro and just left the battery in. It works fine as a buddy box. However, without the battery, nothing.